Fonds primarily documents Armstrong’s social life. They consist overwhelmingly of correspondence for the period 1909-1933. Letters from his professional colleagues, such as Sir William Osler, F.J. Shepard, Edward Archibald, William J. Mayo and others in the Mayo Clinic, are concerned largely with personal greetings, association memberships, or Medical Faculty business, particularly honorary degrees. Armstrong's non-medical correspondents include Lord Beaverbrook, Lord Atholstan, Sir Hugh Allan, Arthur Meighen, George Foster and Herbert Symonds. Topics include politics, Armstrong's war work and honours, some medicals matters, and personal news. Appended to this main series are obituaries and letters of sympathy to Armstrong's widow (1933), six photographs, including one of Armstrong in an operating room, and admission cards and diplomas from Armstrong's student years.

The fonds contains original and typescript letters, manuscript notes, newspaper clippings, journal extracts, reminiscences and more, assembled by Harvey Cushing chiefly between 1920 and 1924 during the course of his research for the biography of William Osler. For the biography, Cushing collected and retyped over 7500 pieces of Osler's correspondence, among which are some original letters.

The fonds is separated into three series: Manuscripts, Working Notes and Osler's Correspondence. It also contains photographs, annual reports, publications, clippings, one watercolor painting, one postcard. Osler's correspondence is further arranged in three subseries based chronologically.

Fonds shows Dr. Philip Franklin's relations and activities with Sir William Osler regarding the Post-Graduate Scheme in England and the American Hospital in England during WWI. The fonds contains letters, telegrams and an agenda and printed material regarding a meeting about the American Hospital.

Zaharoff has just received Osler's letter and will bring its contents to the notice of the important members of the Peace Conference. Although Zaharoff agrees with Professor Tendeloo's opinion that demanding cattle from the Germans would increase their mortality, he does not agree that revolution in the Allied countries is an inevitability.

Letter from Geoffrey Keynes, Darnall's Hall, Weston, Stevenage, England, to William Osler. Keynes is glad that Osler enjoyed his pamphlet on Elizabeth Lyttelton's Commonplace Book. He will send a pamphlet to the Bodleian Library and to Professor Monro [D.B. Munro?].

Letter from L.R. Phelps, Oriel College, Oxford, Oxfordshire, England, to William Osler. Phelps asks Osler to donate money for "the body and soul" of Dr. R.T. Elliott.